1. Field of the Invention
The present invention relates generally to spray formed rapid tools and, more specifically, to a method of reducing distortion in a spray formed rapid tool.
2. Description of the Related Art
It is known to make a spray formed rapid tool. In spray forming, a master model of a desired tool is produced using a free form fabrication technique. This master model is then used to create a ceramic pattern, which is the reverse of the desired tool to be produced. The resulting ceramic pattern is the receptor onto which metal is sprayed to form a deposit in the shape of the desired tool. Typically, the spray forming process uses a wire-arc spraying. In wire-arc spraying, electric current is carried by two electrically conductive, consumable wires with an electric arc forming between the wire tips. A high-velocity gas jet blowing from behind the consumable wires strips away the molten metal, which continuously forms as the wires are melted by the electric arc. The high-velocity gas jet breaks up or atomizes the molten metal into finer particles in order to create a fine distribution of molten metal droplets. The atomizing gas then accelerates the droplets away from the wire tips to the ceramic pattern where the molten metal droplets impact the ceramic pattern to incrementally form a deposit in the shape of the desired tool. The completed desired tool is then mounted and used to produce parts in conventional stamping, die casting, or molding process.
During the spray forming process, the spray formed rapid tool may have a varied temperature distribution across the ceramic pattern and each layer thereof. This can result in distortion of the spray formed rapid tool as shrinkage of the sprayed metal occurs. Recently, there has been a need to create the spray formed rapid tool geometrically accurate. To accomplish this, a number of trial spray runs are conducted to determine ideal spray parameters to obtain a uniform temperature distribution.
Although the above process for making a spray formed rapid tool has worked well, it suffers from the disadvantage that trial spray runs have to be conducted to determine the spray parameters for spraying the spray formed rapid tool. Another disadvantage of the above process is that the spray parameters are achieved by trial and error. Yet another disadvantage of the above process is that to scale between different sized tools with different geometric features, estimation occurs which is undesired. Still another disadvantage of the above process is that the trial spray runs and estimation are time consuming and result in significant development costs for a spray formed rapid tool.